(1) Field of the Invention
The present invention relates to the precise exercise of control over the flow of liquid from a reservoir to a consuming unit and particularly to regulating fluid flow in the form of discrete drops in the intravenous application of the fluid to a patient. More specifically, the present invention is directed to a microcomputer based intravenous fluid flow control system and a restricter for use in such system. Accordingly, the general objects of the present invention are to provide novel and improved methods and apparatus of such character.
(2) Description of the Prior Art
While not limited thereto in its utility, the present invention is particularly well suited for medical applications wherein the flow rate and/or total quantity of a liquid, being fed intravenously to a patient must be precisely controlled. Such precise flow regulation should preferably be accomplished both reliably and accurately. Additionally, a control for a drop-feed intravenous system should be easy to calibrate and operate.
A number of "automatic" IV systems have been proposed in the prior art. A common characteristic of such prior systems resides in the mode of flow control. Since it is desired to employ disposable plastic tubing in an IV set, the flow control "valve" has typically been a constrictor which operates by pinching the tubing. The state of the art of exercising control over the flow rate of a liquid being delivered intravenously to a patient is believed to be exemplified by the disclosures of U.S. Pat. Nos. 3,596,515, 3,601,124 and 3,871,229. As may be seen by reference to these examples of the prior art, an intravenous flow control system will include a reservoir for the fluid to be delivered to the patient, a drop sensor which measures the rate at which the fluid exits the reservoir and a motor operated constrictor which controls the flow rate to the patient in response to an operator selected reference signal and the measured drop rate. Typically, when a difference between the selected flow rate and the drop rate are detected an error signal will be generated. This error signal is delivered to the drive motor of the constrictor and will result in the tube connected to the patient, at a point downstream of the drop sensor, either being more or less compressed to ensure that the delivery rate is maintained at the selected value.
The prior art IV systems, as exemplified by the above-listed patents, possessed certain disadvantages. Foremost among these disadvantages was a limitation on the degree of accuracy which could be achieved since analog circuit techniques were employed. Additionally, system set-up was a comparatively difficult and time-consuming endeavor.